Inorganic peroxygen compounds, especially hydrogen peroxide and solid peroxygen compounds which dissolve in water to release hydrogen peroxide, such as sodium perborate and sodium carbonate perhydrate, have long been used as oxidizing agents for purposes of disinfection and bleaching. The oxidizing action of these substances in dilute solutions is heavily dependent on the temperature; for instance, with H2O2 or perborate in alkaline bleaching liquors, sufficiently rapid bleaching of soiled textiles is obtained only at temperatures above about 80° C. At lower temperatures the oxidizing action of the inorganic peroxygen compounds can be enhanced by adding what are called bleach activators, for which numerous proposals have been disclosed in the literature, principally from the classes of the N-acyl or O-acyl compounds, examples being polyacylated alkylenediamines, especially tetraacetylethylenediamine, acylated glycolurils, especially tetraacetylglycoluril, N-acylated hydantoins, hydrazides, triazoles, hydrotriazines, urazoles, diketopiperazines, sulfurylamides and cyanurates, and also carboxylic anhydrides, especially phthalic anhydride, carboxylic esters, especially sodium nonanoyloxybenzenesulfonate, sodium isononanoyloxybenzenesulfonate and acylated sugar derivatives, such as pentaacetylglucose. By addition of these substances the bleaching action of aqueous peroxide liquors can be increased to such an extent that even at temperatures around 60° C. essentially the same activities occur as with the peroxide liquor alone at 95° C.
Given the concern for energy-saving laundering and bleaching methods, in recent years application temperatures well below 60° C. have gained in importance, in particular below 45° C. down to the cold water temperature, below 20° C.
The prior art has disclosed the use of transition metal salts and transition metal complexes, as proposed for example in European patent applications EP 392 592, EP 443 651, EP 458 397, EP 544 490, EP 549 271 and WO 01/48138, referred to as bleaching catalysts.
It has now been observed that textiles, particularly coloreds, fade after a number of washes. Without wishing to be bound to any particular theory, it is supposed that the catalysts used in the prior art not only catalyze the peroxygen compounds but also directly contact the surfaces to be bleached, such as textile surfaces, and remain at least partly on their surfaces even when the cleaning operation has ended. The transition metal salts containing in the complex compounds are washed out in detectable amounts during the washing operation, and these transition metal salts can then be oxidized and so cause color damage, since they directly contact the article to be bleached: textiles, for example. Mn(II), for example, is demonstrably oxidized to manganese dioxide, MnO2. Manganese dioxide is a not unhazardous oxidizing agent which is very strong, particularly toward readily oxidizable substances, such as organic dye compounds. In the case of the transition metal salts which have been washed out there is a risk, presumably owing to the high reactivity of the oxidizing intermediates formed from them and the peroxygen compounds, of fiber damage and/or color change in colored textiles and, in extreme cases, the risk of oxidative damage to the textiles.
All of the bleaching catalysts known in the art have the disadvantage that they can contact the surfaces of the articles to be bleached to an increased extent, may adhere to those surfaces and may even penetrate the surfaces of the articles to be bleached—for example, they may penetrate into the depth of the textile—so that there is an increased risk of unwanted color changes and in rare cases, with textiles, there may even be holes, as a result of fiber damage.